1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device that involves heating a semiconductor substrate with a high density light source.
2. Background Art
The performance of large scale integrated (LSI) circuits is being improved by increasing the integration density, or in other words, by making elements constituting LSI circuits smaller. As the element size becomes smaller, the parasitic resistance and the short channel effect increase. Thus, the importance of forming a shallow p-n junction having a low resistance is increasing.
A shallow impurity diffusion region can be formed by optimizing ion implantation with a low acceleration energy and subsequent annealing.
In order to decrease the diffusion layer resistance of the impurity diffusion region, annealing for activating the impurity has to be carried out at high temperature. The impurity to be ion-implanted is boron (B), phosphorus (P) or arsenic (As).
However, such an impurity has a high diffusion coefficient in silicon (Si). Therefore, in rapid thermal annealing (RTA) using a halogen lamp, inward and outward diffusions of the impurity ion occurs, and it is difficult to form a shallow impurity diffusion layer.
The inward and outward diffusions can be reduced by decreasing the annealing temperature. However, if the annealing temperature is decreased, the activation rate of the impurity significantly decreases. Therefore, it is difficult to form an impurity diffusion layer having low resistance and shallow junction (20 nm or less) by the conventional RTA using a halogen lamp.
In order to solve the problem, in recent years, as a method of instantaneously supplying energy required for activation, there has been contemplated an annealing method that uses a laser or a flash lamp containing an inert gas, such as xenon (Xe), as a light source. These light sources can complete light emission in a period (pulse width) of 100 milliseconds or shorter or, at the minimum, sub-milliseconds. Therefore, these light sources can activate the impurity ions without substantially changing the distribution of the impurity ions implanted into the upper surface of the wafer.
However, conventional laser annealing and flash lamp annealing (FLA) have the following problem. That is, to sufficiently activate the impurity, the temperature of the upper surface of the wafer easily rises to 1200 degrees C. or higher at a rate of temperature rise of 1×105 degrees C./second or higher. As a result, a temperature difference occurs between the upper surface and the lower surface of the wafer, and the thermal stress in the wafer increases. The increased thermal stress causes damages to the wafer, such as slip dislocation, fracture and deformation, and leads to a reduction in production yield.
In addition, in recent years, cap films, such as a light absorbing film and a reflection reducing film, have been developed in order to prevent the effective annealing temperature from varying due to a difference in pattern size or coverage ratio when a semiconductor substrate with a pattern formed thereon is annealed.
A conventional method of manufacturing a semiconductor device involves forming, on a semiconductor substrate, a translucent film (a cap film) having a lower refractive index than the semiconductor substrate, heating the semiconductor substrate to a temperature equal to or higher than 300 degrees C. and equal to or lower than 600 degrees C., and irradiating the upper surface of the semiconductor substrate with light having a pulse width of 0.1 milliseconds to 100 milliseconds through the translucent film, and the thickness of the translucent film is determined by the peak wavelength of the light and the refractive index of the translucent film (see Japanese Patent Laid-Open No. 2006-278532, for example).
According to the conventional method of manufacturing a semiconductor device described above, occurrence of crystal defects in the semiconductor substrate can be reduced, and a shallow p-n junction having low resistance can be formed.
However, the conventional technique described above does not take damages at the outer perimeter of the wafer (in particular, damages in the vicinity of the bevel part) into account and is not designed to reduce crystal defects, cracks or the like occurring as a result of the FLA process using a flash lamp or the like.